Pitch it at the right level
So should you teach it to primary children? The national curriculum says, "Refine and record their compositions using notation(s) where appropriate" - the bracketed "s" acting as a reminder that there is more than one way of doing it. You can, for instance, encourage and help the children to develop notations of their own - blobs, squiggles, spirals, jagged and smooth lines to indicate different sounds. Dynamics are suggested by making symbols bigger or smaller, high and low pitch by writing them in different positions on the page. This "graphical notation" will take you all the way to the end of key stage 2, and because there are so many other things to do, there seems no reason why a busy non-specialist teacher should become bogged down in technical complication.
Graphical notation is imprecise, of course. Even this, though, can be turned to advantage. Because it gives rough indications rather than accurate instructions, it makes its own creative demands, and every performance is different. Graphical notation is commonly used by modern composers when they want an improvisational element in the performance.
However, most music educators feel that those primary children who are ready and able should be given the opportunity to start on conventional notation, especially when the ability to read music will give them a good start in KS 3.
This need not be too fearsome for non-specialists, or the teachers who dimly remember piano lessons, provided that they start simple and use small steps. There is no more need to plunge into the full grammatical system in teaching music than there is in teaching French. Opposite are some ideas Q though even these can be further broken down.
Some primary music teachers achieve wonders, but do not despairingly measure yourself against high achieving specialists. Be assured that if you can teach a proportion of your children to play simple melodies written in crotchets and quavers on the treble clef on tuned percussion, you will be achieving considerably more than many (perhaps most) primary school teachers.